The present invention relates to diaphragm springs in general, and more particularly to improvements in diaphragm springs or Belleville springs of the type wherein an annular main section is integral with outwardly and/or inwardly extending prongs serving to transmit forces to or from the main section. For example, the prongs can serve to transmit to the main section forces which entail a change in the shape of the main section or to transmit stored energy from the main section to a neighboring component.
A diaphragm spring of the just outlined character is disclosed, for example, in German Auslegeschrift No. 1,475,437. The diaphragm spring which is described and shown in this German publication comprises an annular main section and an annulus of inwardly extending prongs constituting flexible tongues and surrounding a central opening. The neighboring tongues are separated from one another by radially extending slots each of which has a radially innermost portion of constant width and an intermediate portion whose width increases radially outwardly toward the main section. The deepmost portion of each slot is surrounded by a semicircular edge face of the main section. The intermediate portions of the slots are flanked by reinforced portions of the neighboring tongues. Such reinforced portions are formed by bending the material of the tongues from their general planes and in the axial direction of the diaphragm spring. The reinforcement which is achieved with the bent-over portions of the tongues is satisfactory insofar as the stiffening of the major portions of the tongues is concerned; however the reinforced portions cannot adequately reduce the extent of flexing of the radially outermost portions of the tongues in response to the application of axial stresses to their inner end portions for the purpose of changing the conicity of the diaphragm spring. This is due to the fact that the regions where the tongues are subjected to maximum bending stresses are not reinforced at all. Therefore, flexing of the outermost portions of the tongues is quite pronounced which is undesirable under many circumstances, e.g., when the diaphragm spring is used in a friction clutch wherein a release bearing must move through a considerable distance before the tongues are capable of changing the conicity of the main section. Moreover, such construction of the diaphragm spring often entails rapid destruction as a result of breakage of one or more tongues in the regions where their outer end portions merge into the main section. Breakage of tongues in the regions of merger into the main section is highly likely to take place whenever the diaphragm spring of the aforediscussed German publication is subjected to repeated dynamic stresses because of material fatigue as a result of repeated flexing at the innermost part of the main section. The reinforced portions of the tongues do not extend all the way around the innermost portions of the slots between the tongues so that the reinforcements merely stiffen the major part of each tongue inwardly of the region of merger into the main section. Breakage of tongues in a friction clutch, which is installed in a motor vehicle, can result in total destruction of such device with attendant pronounced danger of accidents when the clutch is out of commission.
It is true that the reinforced portions slightly reduce the extent to which the radially innermost portions of the tongues must be moved axially of the diaphragm spring in order to change the conicity of the main section. However, the difference between the extent of axial movement of innermost parts of the reinforced tongues and the extent of axial movement of innermost parts of non-reinforced tongues is small or negligible. As mentioned above, flexing of the outermost portions of tongues in the diaphragm spring of the German publication is still quite pronounced so that the release bearing must cover a considerable distance axially of the clutch before the conicity of the main section is changed sufficiently to disengage the clutch which embodies the diaphragm spring. This is highly undesirable in many types of motor vehicles wherein the space under the hood is at a premium and also on the ground that actuation (disengagement) of the clutch necessitates a longer interval of time.
German Pat. No. 756,351 discloses a friction clutch wherein the diaphragm spring can bias a pressure plate toward a flywheel to thereby establish a frictional torque transmitting engagement between the flywheel and a clutch disc which is placed between the flywheel and the pressure plate. This patent also discloses the possibility of securing the diaphragm spring to the flywheel and of providing the diaphragm spring with portions which bear against the pressure plate when the diaphragm spring is secured to the flywheel. The diaphragm spring of this patent has an annulus of tongues which extend radially inwardly from the annular main section of the diaphragm spring and can be engaged by a release bearing or the like to thereby effect a tilting of the diaphragm spring with attendant disengagement of the pressure plate from the clutch disc. The diaphragm spring is mounted between two ring-shaped seats which are provided on the cover of the clutch, and that portion of the diaphragm spring which bears upon the pressure plate is located radially outwardly of the seats. The cover is secured to the flywheel and transmits torque to the diaphragm spring whenever the flywheel is driven by the internal combustion engine a motor vehicle or the like. The diaphragm spring is installed in stressed condition so that it normally bears against the pressure plate and urges the latter against the clutch disc. Thus, the friction clutch of this German patent is normally engaged and is disengaged in response to axial shifting of a pressure transmitting element or a release bearing whereby such pressure transmitting element or release bearing acts upon the radially innermost portions of the tongues to pivot the diaphragm spring not unlike a two-armed lever whose fulcrum is defined by the two seats on the cover. This causes the portion of the diaphragm spring radially outwardly of the seats to pivot away from the pressure plate whereby the pressure plate releases the clutch disc which is then free to rotate independently of the flywheel and/or vice versa.
A somewhat different friction clutch is disclosed in French Pat. No. 1,281,320. In the clutch of this French patent, the diaphragm spring again acts not unlike a two-armed lever and serves to urge a pressure plate against a clutch disc so that the latter is held in requisite torque-receiving engagement with a flywheel or the like. However, the radially outermost portion of the diaphragm spring bears against the flywheel (i.e., against a component which is not designed to perform axial movements) and the pressure plate is movable axially of the flywheel together with the cover and the diaphragm spring. Axial shifting of the diaphragm spring (together with the pressure plate and the cover) with reference to the flywheel takes place when the clutch is to be disengaged so as to release the clutch disc which is installed between the pressure plate and the flywheel.
The friction clutch of the aforementioned German patent (especially the embodiment which is shown in FIGS. 1 and 2 of this patent) has been on the market for several decades and has found widespread acceptance in the automobile industry. However, the patented clutch still exhibits a number of drawbacks, especially as concerns the assembly of its parts, the cost of manufacturing the parts, the number of parts and the mode of operation.